Earth inductor compass



June 24, 1941. c. WASHBURN EARTH INDUCTOR COMPASS Filed March 14, 1939 2 Sheets-Sheet 'l J 6 e 1 0 O J| J w M 5| mm m fob Clarence L.Wa.s]zburrz.

S3341 CW A A A A 0 Q B June 24, 1941. L WASHBU'RN 2,246,558

EARTH INDUCTOR COMPASS Filed March 14, 1939 2 Sheets-Sheet 2 COILCURRENT 12 62 @269 Fig.6.? zwe a A W W AMMETER CURPENT(FlG5B -6 A I A 2- a 9 B B B ClarenceL.Wa$/1burw.

Patented June 24, 1941 2,246,558 mam mnuc'ron ooMrAss Clarence L. Washburn, Silver Spring, Md, as-

signor to Washington Institute of Technology, Inc., Washington, D. (3., a corporation of Delaware Application March 14, 1939, Serial No. 261,795

7 Claims.

This invention relates broadly to the art of determining r indicating direction by employing the lines of force of the earths magnetic field and, more particularly, is intended to provide a new and improved deviceof the type or class known in the art as the earth inductor compass. 1

Direction indicating devices of this type are well-known in the art. The operation of these devices is based upon the fact that if a coil is rotated in the earth's magnetic field a minute current is generated in the coil. It was recognized at an early stage in the development of the art that if this current is taken from the coil by a commutator and diametrically-opposed brushes, the current across the brushes will be proportional to the angular disposition of a line connecting the brush contacts with respect to the direction of the earths magnetic field. In the early patent to Bliss, No. 1,047,157, this principle was illustrated and means were provided for moving the brush plane-*in. order to cause the current across the brushes to provide a directional indication by operating-.theindicating pointer of a milliammeter'or millivoltmeter.

I have found that earth inductor compasses constructed and operated in the manner taught in the prior art are subject to certain disadvantages. One of these is due to the construction which has heretofore been employed and involving the connection of a rotating commutator to the coil system of the compass and the provision of relatively fixed brushes in wiping ,engagement with this rotating commutator and which may be oriented with respect to the direction of the earth's magnetic field in order to produce zero brush current at any heading of the craft on which the compass is mounted. This construction'fails to provide a consistent, reliable contact for such minute currents as are produced by the rotating coil, and this deficiency in these devices has been recognized as'one of the principal reasons for the imperfect operation of these devices.

It is the principal object of the present invention to provide an earth inductor compass adjusted to zero for any desired heading of the craft.

A further object of the invention is to provide an improved and compact earth inductor com-v pass structure having operating and constructional advantages over those of the prior art.

Other objects and features of novelty of the invention will be apparent from the following description and the annexed drawings, it being understood, however, that the invention is not limited in any way by such description and drawings or otherwise than by the appended claims. Referring tothe drawings, in which similar reference numerals refer to like parts:

Fig. 1 is a view, which is partly in section and partly diagrammatic, of an earth inductor compass system formed according to my invention; Fig. 2 is a sectional view taken on the line 22 of Fig. i;

Fig. 3 is a circuit diagram of the electrical connections of the compass;

operation of the invention.

which is so constructed and operated that the deficiency referred to will be entirely obviated.

In carrying out this object I provide a structure 5 in which the brush assembly is rotated with the pick-up coils-and co-operates with a series of 'relatively fixed insulated segments which may L be oriented with respect to the earths'magnetic -fleld, -'a'nd from which currents are taken which,

by proper orientation of the commutator. are

One structural embodiment which the method and means of the present invention may take is illustrated in Figs. 1 and 2 of the annexed drawings and, by reference to such figures, it will be seen that there is provided a driving motor i, which is suitably connected to a source of electric potential, and on the shaft 3 of which there are mounted a plurality of supporting rods 6 which estend radially from the shaft 3. Each of these rods supports a winding 5 of metallic wire, there being preferably provided four such windings mounted on an equal number of rods which are arranged at intervals about the shaft 3. The motor 5 is preferably disposed above the coil assembly and is contained in a housing 6 forming a magnetic shield. The shaft 3 extends downwardly from the motor and the rods 4 and coils 5 are arranged at its lower end. A housing l surrounds the rod and coil assembly, which may. be denoted as'the armature of the compass, and this housing is so proportioned and arranged that the armature may rotate therein when the motor and shaft are operated. The shaft 3 is preferably somewhat elongated in order to provide a space between the housings Gland l and this space is enclosed and surrounded by a housing 8. It will be apparent that the three housings 6, l and 8 may be formed the art, the motor may be operated to cause the shaft 3 and the armature of the compass to rotate, the rotation of the windings 5 in the earths magnetic field causing currents to be induced therein which are employed to provide the field. This adjustable assembly, which may be.

mounted on the upper surface of the armaturehousing 1 comprises an annular worm gear H which surrounds the shaft 3 and on the upper surface of which are carried two superposed, an-

nu-lar insulating members l2, portion of the upper surface of the upper member I3 is recessed to receive a plurality of arcuate metallic segments Ila, Mb, I40 and Md which are insulated from each other at l5 and which provide a segmental ring-shaped contact strip, eachof the parts of which is insulated from the remaining parts. The upper surfaces of the segments H! are flush with each other and, preferably, with the upper surface of the upper insulating member I3. In the embodiment of the invention which is illustrated, four separatedsegments II are provided but any other number of segments maybe employed.

Extending outwardly from the outer peripheries of the two insulating members [2, l3 are two vertically-spaced contact rings l6, l1. These rings are insulated from each other and the ring I6 is connected to commutator segment Ha by lead I8, while ring I1 is connected to segment I40 by lead l9, whereby the two contact rings are separately connected to diametrically opposed commutator segments. The two contact rings [6, I! are connected to the opposite terminals of a zero-centermilliammeter or millivoltmeter type indicating instrument It] by suitable leads. A sensitivity control, in the form of a variable resistance 20 may be connected between the terminals of the indicator in order to control the magnitude of the deflection of the meter.

Means are provided by the invention for supplying to th commutator segments I 4, and from thence to the contact rings and the terminals of the indicating device, the currents induced in the windings 5 of the armature of the compass. Such means comprise a brush assembly which is rigidly connected to the shaft 3 above the commutator assembly and which comprises a support which surrounds the shaft and to l3. The inner which are connected the one ends of four brushes of these windings are connected to the opposite brushes 26a and 26c by suitable leads. In the same manner, the opposite windings 5b and 5d are connected in series and their opposite ends are connected to the opposed brushes 2% and 2612. It will be apparent that, by reason of the .rigid connection of the brushes and the armature windings to the shaft 3, these elements will be rotated together with the shaft.

Means are provided for orienting the commutator assembly to position the segments thereof in any desired angular relation to the direction of the earths magnetic field. Such means comprise a worm'gear 3|, which meshes with the annular worm gear II and which is connected, as by flexible shafting 32, to a crank 33 which is adapted to be manually operated. A counter 34 is provided for indicatingthe azimuthal position of the commutator segments, and this counter is preferably driven from the shaft 32 through one-to-one gearing 35.

The compass structure described hereinbefore may be mounted in gimbals and may, if desired.

xbe associated with gyroscope means, all in order to maintain the compass in such a position that the armature windings 5 will be affected only by the horizontal component of the earths magnetic field. If desired, and as is preferred, such mountings and gyroscope means may be dispensed with and the compass may be provided with means, as indicated at 30, which constantly compensate for the vertical component of the earths magnetic field. Such means are fully described and illustrated in Letters Patent No. 2,054,318, issued to Ross Gunn, and will not be further illustrated or described in this application.

The mechanical operation of the described I tator segment will cause the currents in the coils to be transmitted to the segments, to the contact rings l6, l1 and, from thence, to the ,opposite terminals of the indicating instrument. Operationof the crank 33 will caus the entire commutator assembly to be rotated about the shaft 3 to thereby orient the commutator segments to any desired position, \at the same time operating the counter 34 in order to provide an indication of the azimuthal position of the line joining the midpoints of the two commutator segments which are electrically connected to the contact rings 16,11.

The manner in which the currents induced in thearmature windings are caused to operate the indicator II] in order to produce an indication of deviation from a pre-determined course will be understood more clearly by reference to Figs. 4 to 9 of the drawings. In Fig. 4 there are illustrated parallel lines denoting the lines of force of the earths magnetic field, and a coil disposed in that field and .extending along a line AC which is at right angles to the direction of the lines offorce of th field. If the coil is rotated in the direction of the arrow of Fig. 4, it will be seen that during 'the first increment of its movement, no current .will be induced in the coil because of its movement parallel to the lines of force, while during the first of movement the current in the coil will increase to a maximum. Rotation of the coil through. 360 4 These brushes, traveling over and in electricalengagement with the commuwill cause a current to be induced therein which may be represented by the sine curve of Fig. 5, it being noted that the direction of flow of, current in the coil reverses once during each complete revolution thereof; and that there are two points of -zero current and two points of maximum current during each revolution.

If the terminals I, 2 of the coil are electrically connected to two arcuate commutator segments which are so positioned that a line joining their midpoints is at right angles to the direction of the magnetic lines of force, as illustrated in Figs. 6a, 6b, 6c and 6d, then, as the coil rotates, equal currents will be alternately supplied in opposite directions to an ammeter which is connected between the two segments, thereby producing a zero indication of the meter. Having reference to these figures and to Fig. 7 it will be seen that'as the' coil. rotates so that its terminal I passes from point A to point B, the induced current in the coil will flow from terminal 2 to' terminal I, will increase from zero to a maximum and will flow to ammeter A in the direction of arrow 0., this current being represented by curve AB of Fig. 7. During the next 90 increment of movement the direction of current fiow in the coil will remain the same, but, as illustrated in Fig. 6b the flow of current to the ammeter will be reversed and is now in the direction of arrow b,.this current being represented by the curve B0 of Fig. 7. During the next 90 movement of the coil, as illustrated in Fig. 6c, the direction of flowof current in the coil will be reversed and current will flow to the ammeter in the direction of arrow a, this current being represented by curve CD of Fig. 7. During the final 90 of movement of the coil, as illustrated in' Fig. 6d, the direction of current flow in the coil remains the same but current is now supplied to the ammeter in the direction of arrow b and is represented by curve DA of Fig. 7.

It will be seen by reference to Fig. 7 that during one complete. revolution of the coil the direction of current flow to the ammeter willbe reversed four times and that current supplied in the direction of arrow a will equal that supplied in the direction of arrow b. If the coil is rotated at suificient speed" and the meter is suitably. damped the currents supplied in opposite directions will cause a continuous zero indication to be provided, and this condition will prevail so long as the commutator segments are maintained in the described relation to the lines'of force of the earths magnetic field.

Any deviation of the aforesaid relation of the commutator segments with respect to the earth'smagnetic field will cause a deviation of the indicating means from its zero-center position. This eflectmay be illustrated by reference to Figs. 8a, 8b, 8c, 8d and 9. As illustrated in these figures, the segments are moved to a position in which a line joining their midpoints bears some relation ,to the direction of the lines of force of the earth's magnetic field which is not a right angle, an ammeter A is connected between the two segments, and a coil'having its ends electrically connected to the segments is rotated in the earth's magnetic field. If the coil is rotated counterclockwise from the position illustrated in Fig. 8a, i. e. from an initial position which is at right angles to the direction of the magnetic lines of force,-the induced current will flow in the same direction therein during rotation of-the coil through 180 and, during such rotation, current will flow to the ammeter in the direction of arrow a, the latter part of this movement being illustrated in Fig. 8b. The current supplied to the ammeter during the first 180 of rotation of the coil is represented by the curve ABC of Fig. 9. Further rotation of the coil will cause the direction of how of current induced therein to be reversed, the current now flowing in the coil from terminal I to terminal 2, as illustrated in Figs. 8c and 8d. At the same time, the relation of the terminals of the coil to the commutator segments is reversed, and the induced current will continue to flow to the ammeter in the direction of arrow a. This current will increase from zero,

when the coil lies along the line AC, to a maximum when the coil is in the position BD and will decrease to zero when the. coil returns to theposition CA. This current is represented by curve CDA of Fig. 9. It will be seen that current is supplied to the ammeter in the direction of arrow a during the entire rotation of the coil,

thereby producing a "constant deflection of the pointer of the indicating meter, showing that the craft carrying the compass is off of its predetermined "course and must be guided in such a way as to cause a line joining the midpoints of the commutator segments to again lie at right angles to the direction of the lines of force of the earths magnetic field.

While I have illustrated and described one embodiment which my invention may take it will be apparent to those skilled in the art that various changes and improvements may be made,

particularly with reference to the structural aspect of the invention and the arrangement said'coils is delivered to one of said pairs of brushes, and a plurality of metallic segments which are slidably engaged by said brushes and are insulated from each other and which form an annular ring which is fixed with respect to the rotating coils and brushes but which is so mounted that it may be oriented to cause the segments to assume different positions with respect to the direction of the earths magnetic field. 1

2. A compass generator comprising a rotatable armature, means for rotating said armature, means for collecting electric energy generated in said armature comprising a normally fixed ring having a plurality of separated segments and being mounted for adjustment about its axis, and

rotating means adapted-to be electrically connected to said armature and to rotate therewith and being in electrical engagement with the segments of said ring.

3. A compass generator comprising a rotatable armature, means for rotating said armature,

to said armature and to rotate therewith and which are in sliding electrical engagement with the segments of said ring.-

4. A compass generator comprising a rotatable armature, means for rotating said armature means for collecting electric energy generated in said armature comprising a normally fixed ring formed of a plurality of separated segments and being mounted for adjustment about its axis, and a plurality of pairs of brushes having portions in sliding electrical engagement with said segments, each oi said pairs of brushes being adapted to be electrically connected to one of the windings of said armature and to be connected to said armature to rotate therewith.

5. A compass generator comprising a rotatable armature, means for rotating said armature,

means for collecting electric energy generated in said armature comprising a normally fixed ring formed of a plurality of. separated arcuate segments and being mounted for adjustment about its axis, a plurality of pairs of brushes mounted for rotation with said armature, each of said pairs of brushes being adapted to be electrically connected to one of the windings of said armature and having portions in sliding electrical engagement with the segments of said ring, and a contact member connected to each of the segments of said ring.

6. A compass generator comprising a rotatable armature, means for rotating said armature,

- means for collecting electric energy generated in I wheel.

said armature comprising a normally fixed ring formed of a plurality of separated arcuate segments which is mounted for adjustment about its axis, a rotatable assembly comprising a plurality of pairs of brushes connected to said armature to rotate therewith, each of said pairs trically connected to the windings thereof, a gear wheel arranged concentrically of the axis of r0- tation of the brushes, a plurality of separated metallic segments carried by said gear wheel and insulated therefrom and arranged to form an annular series thereon and being disposed in sliding electrical engagement with said brushes,

said gear wheel and contact members being mounted for adjustment about the axis of said gear wheel, and means for rotating said gear CLARENCE L. WASHBURN. 

